Radioactive diamond composition



United- States Patent C) 3,125,418 RADIOACTIVE DIAMOND COMPOSITIGN Robert H. Wentorf, Jr., Schenectady, N.Y., assignor to General Electric Company, a corporation of New York No Drawing. Filed Mar. 20, 1961, Ser. No. 96,702 2 Claims. (Cl. 23209.1)

This application is a continuation-in-part of my earlier application Serial No. 562,585, filed January 31, 1956, now U.S. 2,996,763, issued August 2.2, 1961, and assigned to the same assignee as the present invention.

This invention relates to radioactive diamond material and to the preparation thereof. More particularly, this invention is concerned with diamonds containing a surface coating of a radioactive metal and to the preparation thereof.

As is well known in the art, natural diamonds, particularly natural diamonds of the industrial variety, readily acquire and retain a charge of static electricity. This generally occurs when natural industrial diamonds come into contact with each other or with some other surface. The static charge on industrial diamonds, results in a number of problems in their use. Thus, when an attempt is being made to sort industrial diamonds, it is found that the static charge seriously interferes with the segregation of the diamonds into various size groups and interferes with the moving of the diamonds from one location to another. In addition, when natural diamonds are applied in uses such as in bearings or in grinding tools, the charge on the surface of the diamond tends to attract dust or other undesirable particles of matter to the surface of the diamond. When diamonds are used as bearing materials such as in time pieces and other delicate mechanisms, the dust or other particles attracted by the static charge on the surface causes abrasion of the surface supported by the bearing and, therefore, reduces or destroys the efiiciency of the bearing. Where diamonds are used in industrial grinding tools, it is found that the static charge on the diamond surface causes particles of dust and of metal to adhere to the surface of the diamond and interfere with proper and accurate grinding.

An object of the present invention is to provide a diamond material which does not retain a charge of static electricity for any substantial period of time.

Another object of the present invention is to synthesize diamond material of the type described from non-diamond carbon.

These and other objects of my invention are accomplished by providing a radioactive diamond material comprising a diamond having a radioactive metal in adherent relation to the surface thereof. This radioactive diamond material is formed by a method which comprises subjecting non-diamond carbon to a pressure of at least 40,000 atmospheres, e.g. from 55,000 to 110,000, and preferably about 65,000 atmospheres, at a temperature of from 1200 to 2200 C. or higher in the presence of (1) the radioactive material, preferably a radioactive metal, and (2) at least one metal selected from the class consisting of group VIII metals of the periodic table, and chromium, tantalum, manganese, and compounds of these metals which decompose to the metallic state under the conditions of the reaction, as well as alloys of these metals.

The termradiactive metal is used in the present application in its usual sense to refer to a metal which has the property of spontaneously emitting alpha, beta, or gamma rays by the disintegration of the nuclei of the atoms of the metal. As is well known, the radiation emitted by radioactive elements causes ionization of the medium surrounding the radioactive material or the medium through which the alpha, beta, or gamma rays pass. It is further understood that when, for example, air is ice ionized by rays from a radioactive material, the ionized air becomes, to some extent, a conductor of electricity. Thus, where the diamond material of the present invention acquires -a static charge, the radioactivity of the surface layer of the diamond material causes ionization of the air or other medium surrounding the diamond material and this ionized air or other material carries away the static charge from the surface of the diamond material, rendering the diamond material electrically neutral.

As can be seen from the description of the ionization of the medium surrounding the diamond materials of the present invention and the discharging of the static charge on the diamond material, the diamond material of the present invention is free from the problems associated with natural diamonds. Thus, since the diamonds of the present invention do not retain a static charge, they may be sorted Without the difficulty caused by any static charges on the material. In addition, when the diamonds of the present invention are used as bearings, they will have no tendency to attract dust or other abrasive particles to their surface. Furthermore, when the diamond material of the present invention is employed as abrasive material in abrasive wheels, there is again no tendency for any static charge to accumulate on the diamonds and therefore there is no tendency for the grinding wheel to attract particles of metal which may interfere with the accurate use of the grinding wheel.

In U.S. Patents 2,947,609 and 2,947,610, issued August 2, 1960, and assigned to the same assignee as the present invention, there are described methods for making diamonds in which non-diamond carbon is subjected to a pressure of at least 50,000 atmospheres and preferably from 65,000 to 110,000 atmospheres, at a temperature of from 1200 to 2000 C. in the presence of a catalyst which is a metal or alloy of said metal selected from the class consisting of group VIII metals of the periodic table, and chromium, sodium, tantalum, aluminum, manganese, and compounds of these metals which decompose to a metallic state under the conditions of the reaction. The process of the present invention is carried out by the same method as that described in the aforementioned two patents except that the reaction is carried out also in the presence of a radioactive material.

The process of the present invention may be carried out in \any type of apparatus capable of producing the pressures required at the temperature required. However, I prefer to employ apparatus of the type described in Hall, U.S. Patent 2,941,248, issued June 21, 1960, and assigned to the same assignee as the present invention. The disclosure of this Hall patent is hereby incorporated by reference into the present application. The apparatus disclosed in the aforementioned Hall patent is a high pressure device for insertion between the platens of a hydraulic press. The high pressure device consists of an annular member defining a substantially cylindrical reaction area, and two conical, piston-type members designed to fit into the substantially cylindrical portion of the annular member from either side of said annular member. A reaction vessel 33 which fits into the annular member may be compressed by the two piston members to reach the pressures required in the practice of the present invention. The temperature required is obtained by any suitable means, such as, for example, by induction heating, by passing an electrical current through the reaction vessel, or by winding heating coils around the reaction vessel.

The reaction vessel or cylinder 33 described in the Hall patent referred to above, may be formed of any of the conventional materials of construction or of graphite. Where the reaction vessel is constructed of a metal, it is convenient to employ one of the metals which acts as a catalyst in the present invention. This vessel may then be filled with non-diamond carbon and a radioactive material and compressed so that the metal present in the vessel will serve as a catalyst for the transformation to diamond. Where the reaction chamber or vessel is formed of graphite, it may be filled with a mixture of the catalyst material and the radio-active material and the compression of the graphite vessel with the catalyst and radioactive material at the pressures and temperatures required by the present invention results in the transformation of the nondiamond carbon into the radioactive material of the present invention. The reaction vessel or chamber may also be formed of a radioactive metal, where this is the case, the reaction vessel is filled with non-diamond carbon and catalyst material and compression of the reaction vessel at the proper pressure and temperature causes transformation of the non-diamond carbon into the radioactive material of the present invention. Regardless of the material of construction of the reaction vessel, the non-diamond carbon, the catalyst, and the radioactive material may be admixed inside the vessel. Thus, mixtures of powdered non-radioactive graphite, powdered catalyst, and powdered radioactive material may be employed as a charge in the reaction vessel and the compression of the vessel and charge at the required temperature effects transformation to radioactive diamond material.

In the preferred embodiment of my invention, I employ a reaction vessel 33 comprising a cylinder of graphite having a hollowed out cylindrical center portion, the axis of the center portion being coaxial with the axis of the reaction vessel. Into this graphite reaction vessel are placed cylinders or disks of graphite, the catalyst, and the radioactive material. T his reaction vessel is sealed at its ends by metallic disks which may be formed of any material of construction inert under the conditions of the reaction or it may be formed of a catalyst metal or a radioactive material. If desired, plugs of non-diamond carbon or metal may be placed in the ends of the reaction vessel before sealing. This reaction vessel is then placed in the apparatus described in the above-mentioned Hall patent and subjected to the elevated temperature and pressure required to effect the transformation to radioactive diamond material. Alternatively, instead of employing a reaction vessel, a cylinder of carbonaceous material, such as graphite, may be sandwiched between two disks, each formed of a radioactive metal, this sandwich in turn being sandwiched between two other disks formed of a metal which acts as a catalyst for the transformation. The sandwich is then placed in the high pressure apparatus and subjected to the conditions required to cause the transformation to radioactive diamond material. As -a further alternative, a metallic reaction vessel may be filled with carbonaceous material in powder or solid form and the catalyst and radioactive material for the reaction may be supplied by admixing it with the powdered carbon or by forming end disks of either of these materials to seal the reaction vessel. This assembly is then subjected to the pressures and temperatures required. A reaction vessel may also be formed by compressing a mixture of nondiamond carbon, catalyst, and radioactive material until a cylinder is formed which fits into the substantially cylindrical aperture described in the above-mentioned Hall apparatus. Again, this latter apparatus may be employed in the usual manner at elevated temperatures and pressures to effect the transformation to radioactive diamond material.

In carrying out the process of the present invention, the temperature in the reaction vessel may be measured by a thermocouple located adjacent the reaction vessel previously mentioned. In carrying out this process, the time of reaction required to convert the reaction mixture into radioactive diamond material may vary from a few seconds up to several minutes or more depending on the particular charge to the reaction vessel. However, regardless of the charge to the reaction vessel, I have found that the radioactive diamond material of the present invention is formed within two to five minutes. Instead of observing the time which the reaction vessel is maintained at the reaction temperature, I may alternatively observe the progress of the reaction by the method described in Hall Patent 2,947,608 issued August 2, 1960, and assigned to the same assignee as the present invention. This latter Hall patent is hereby incorporated by reference into the present application. By the process of this Hall patent, the mixture of non-diamond carbon, catalyst, and radioactive material, is first subjected to a pressure of at least 5 0,000 to 75,000 atmospheres (depending on whether a metal or alloy is used as catalyst) and subsequently sufficient heat is applied to the mixture for sufficient time to cause an inflection in the electrical resistance of the mixture. When the inflection in the electrical resistance of the mixture occurs, the transformation of the mixture to the radioactive diamond material of the present invention has occurred.

The radioactive materials which may be employed in the practice of the present invention include all of the naturally occurring radioactive metals such as uranium, thorium, bismuth, rhenium, lutecium, samarium, indium, rubidium and potassium. Also included within the radioactive metals employed in the practice of the present invention may be mentioned the deacy products of naturally radioactive materials as Well as all of the well known radioactive isotopes of metals. Included within these latter two groups of radiocative materials may be mentioned, for example, the radioactive isotopes of protactinium, actinium, neptunium, plutonium, radium, francium, radon, cobalt, etc.

In addition to the radioactive isotopes specifically mentioned above, it should be understood that other artificial metallic isotopes are also included within the scope of the present invention. As an illustration of other isotopes within the scope of the present invention, reference is made to all of those radioactive isotopes of metals listed in Appendix 6 at page 464 of Nuclear Radiation Physics, by Lapp and Andrews, Prentiss-Hall Inc., New York (1948).

In preparing the radioactive diamond material of the present invention, the proportions of the three ingredients employed are not critical, and I have found that suitable radioactive diamond material has been formed regardless of the relative concentration of the non-diamond carbon, the catalyst, and the radioactive metal. However, in the preferred embodiment of this invention, it is preferred to have the ingredients present in the proportions of about six parts by volume of non-diamond carbon, six parts by volume of catalyst, and one part by volume of the radioactive metal. Regardless of the proportions of ingredients and the physical location of the various ingredients in the reaction vessel, it has been found that the resulting product comprises diamond having in adherent relation to the surface thereof a radioactive metal.

The thickness of the radioactive layer on the outside of the diamond varies to a minor extent with the proportions of ingredients employed in the reaction. However, regardless of the proportions employed, I have found that the thickness of the radioactive metal layer lies within the range of about 0.5 to 5.0 microns. The relative weight of the diamond to the radioactive layer is dependent upon a number of factors, including the density of the radioactive material, the concentration of the reactants employed in forming the diamond material, and the size and shape of the diamonds. Because of these variables, it is impossible to specify an exact ratio of the weight of the carbon in the diamond to the weight of the radioactive metal. However, I have obtained satisfactory products where the ratio of the weight of diamond to the weight of radioactive metal varied from about 10 to 20.

The type and intensity of radiation emitted from the radioactive diamond material of the present invention is, of course, dependent upon the type of radioactive material employed. Thus, where the radioactive material employed is thorium, the radiation from the radioactive diamond material is that well known radiation emitted by thorium. Similarly, where the radioactive material is a material other than thorium, the radioactivity is that charcteristic of that other radioactive material. The half life of the radiation from the radioactive diamond materials is also dependent on the radioactive metal employed and is the same as the half life of the radioactivity commonly observed from said radioactive metal.

Since the radioactive materials of the present invention are similar to other radioactive materials, some degree of care is necessary in handling the products of the present invention. The degree of care required in handling theradioactive diamond materials is similar to that degree required in handling the radioactive metals themselves.

The following examples are illustrative of the practice of my invention and are not intended for purposes of limitation.

In the following examples, the reaction vessel consisted of a cylindrical graphite member having a cylindrical aperture therethrough, the axis of the aperture being coaxial with that of the cylinder. The walls of the cylindrical graphite member were approximately one-sixth as thick as its diameter and the length of the cylinder was approximately three to five times its outside diameter.

Example 1 Into the reaction vessel described were placed two nickel cylinders to act as a catalyst for the reaction, two thorium disks as the radioactive metal, and one graphite cylinder which was to be converted to diamond. These reactants were assembled in the reaction vessel in the following order: a nickel cylinder, a thorium disk, the carbon cylinder, the second thorium disk, and the second nickel cylinder. The diameters of each of these rods were substantially equal to the internal diameter of the reaction vessel and the length of each rod was selected so that there was present in the reaction vessel about 12 parts by volume of carbon, 12 parts by volume of nickel, and one part by volume of thorium. The reaction vessel was then sealed at each end with a tantalum disk and subjected to a pressure of about 95,000 atmospheres at a temperature of about 1500 C. for about six minutes. At the end of this time the reaction vessel was allowed to cool, the pressure was released, and the radioactive diamond material was separated fromthe matrix in which it was formed by solution of the matrix in fuming red nitric acid. From a measurement of the radioactivity of the diamond material, it was determined that the thorium content of the radioactive diamond material was approximately 5 percent by weight based on the total weight of the diamond material. This is equivalent to about 2.5 thorium atoms per thousand carbon atoms and represents a film about 0.75 micron thick of thorium on the surface of the diamond. The fact that the thorium was present as a surface layer on the diamond was established by boiling the radioactive diamond material just described in aqua regia for 24 hours, after which time the diamond material exhibited no further radioactivity despite the fact that the appearance of the diamond material was unchanged.

Example 2 The procedure of Example 1 was repeated except that the ratio of the volume of the various reactants was as follows: 6 parts by volume of carbon, 6 parts by volume of nickel, and one part by volume of thorium. After the reaction vessel had been exposed to a pressure of about 95,000 atmospheres at a temperature of about 1500 C. for five minutes, the resulting radioactive diamond material was isolated and found to have a radioactivity corresponding to 10 percent thorium by weight, which is equivalent to 5 thorium atoms per thousand atoms and represents a film of thorium about 1.5 microns thick.

Although the catalyst and the radioactive materials which may be employed in the practice of the present invention have been described only in terms of pure metals, it should be understood that alloys and compounds of these metals which decompose under the conditions of the reaction may also be employed. Thus, compounds of the catalyst and of the radioactive metal which decompose into pure metal under the conditions of the reaction include, for example, the carbides, sulfides, carbonyls, cyanides, ferrotungstates, ferritungstates, oxides, nitrides, nitrates, hydrides, chlorides, molybdates, arsenates, acetates, oxalates, carbonates, borates, chromates, phosphates, phosphides. permanganates, silicates, sulfates, tungstates, etc. Specific examples of decomposable compounds usable as catalysts in the present invention include ferrous sulfide, iron carbonyls, palladium chloride, chromium carbide, tantalum hydride, sodium fluoride, nickel perman ganate, cobalt acetate, nickel sulfate, etc. Examples of alloys are found in the aforesaid US. Patent 2,947,609. Examples of radioactive compounds which may be employed include, for example, uranium fluorides, thorium carbides, radium sulfates, etc.

Although the above examples have described the reaction of the present invention only at a pressure of 95,000 atmospheres and a temperature of about 1500" C., it should be understood that any pressure in excess of 40,000 to 50,00 atmospheres is satisfactory for the practice of this invention. My preferred pressure range is from about 65,000 to 110,000 atmospheres. Similarly, my temperature range may vary from 1200 C. to 2000 C., and preferably from about 1400 C. to 1800 C.

The radioactive diamond material of the present invention is useful for all of those uses to which diamonds are commonly put. In addition, this radioactive diamond material is particularly useful as the abrasive medium in an abrasive wheel. In addition, the radioactive diamond material of the present invention is particularly suitable for use as a bearing surface in applications where the bearing must withstand an extremely high load and where the dust which would be attracted by an ordinary diamond bearing would ruin the effectiveness of the bearing action. Thus, the radioactive diamond materials of the present invention are particularly suitable as jewels for use in clocks, timers, and the like where dust might interfere with the accuracy of the device.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. A manufactured radioactive diamond material comprising a diamond having a radioactive adherent metallic surface of from about 0.5 to 5 microns in thickness.

2. A composite article comprising manufactured diamond having a radioactive metallic surface layer of from about 0.5 to 5 microns in thickness.

References Cited in the file of this patent UNITED STATES PATENTS 1,154,127 Rasehorn et a1 Sept. 21, 1915 2,048,490 Bilstein July 21, 1936 2,264,683 Smith Dec. 2, 1941 2,678,400 McKay May 11, 1954 2,973,292 Yanko et al Feb. 28, 1961 OTHER REFERENCES Schreiber, A.: Chemical Process Control With Radioactivity, Nucleonics, January 1948, pages 38-39.

Industrial Applications of Radioactivity, Electronics, April 1948, pages 78-79.

Calkins, G.: Radioisotopes in Industry, Chemical and Engineering News, June 18, 1951, volume 29, No. 25, page 2457. 

1. A MANUFACTURED RADIOACTIVE DIAMOND MATERIAL COMPRISING A DIAMOND HAVING A RADIOACTIVE ADHERENT METALLIC SURFACE OF FROM ABOUT 0.5 TO 5 MICRONS IN THICKNESS. 